The invention relates to a stabilized microwave oscillator.
The oscillators according to the invention have a structure similar to parametric amplifiers. It provides a microwave stabilized on a frequency f.sub.o.
Parametric amplifiers have three essential parts corresponding to three frequencies: signal frequency f.sub.s, pump frequency f.sub.p and image or idler frequency f.sub.o. They cooperate with one another in the manner described below.
A first source of signal frequency f.sub.s and a second source at the pump frequency f.sub.p are arranged in parallel at the terminals of a nonlinear or parametric capacitor, whose value C(V) varies with the voltage applied to its terminals. Capacitor C(V) behaves like a negative resistance for the frequency signal f.sub.s which is amplified. At the same time a signal at frequency f.sub.o, equal to the difference between the two frequencies f.sub.p and f.sub.s, (f.sub.o =f.sub.p -f.sub.s) appears in a third branch also connected in parallel at the terminals of the capacitor.
The frequency f.sub.p or pump frequency is generally much higher than the signal frequency f.sub.s, and the power level at the frequency f.sub.p is much higher than that of the signal at the frequency f.sub.s. The source at the pump frequency f.sub.p modifies the impedance at frequency f.sub.s and causes amplification on said frequency f.sub.s. Frequency f.sub.o is itself much higher than frequency f.sub.s.
The same arrangement is used in the invention for another purpose, namely that of stabilizing an oscillation frequency. The frequency stabilized in the device according to the invention is frequency f.sub.o. No further description will be given here of the theory of parametric amplifiers and in this connection reference can be made to the work by W. H. Louisell "Coupled Mode and Parametric Electronics", Wiley and Sons, New York 1960.
It is merely pointed out that in the case of the invention, this arrangement makes it possible to use for the stabilization of frequency f.sub.o, those elements resonating at a much lower frequency f.sub.s, and which are therefore able to give a higher quality factor. The signal at frequency f.sub.o is obtained by frequency transposition or conversion with a signal-to-noise ratio very close to that which would be obtained with a frequency directly stabilized by the circuit having a high quality factor.